The field of the present disclosure relates generally to gas turbine engines and more specifically, to methods and systems for cooling gas turbine engine rotor assemblies.
At least some known gas turbine engines include a rotor assembly including circumferentially-spaced turbine blades. Each turbine blade, sometimes referred to as a bucket, includes an airfoil that extends radially outward from a platform. Each turbine blade also includes a dovetail that extends radially inward from a shank that extends between the platform and the dovetail. The dovetail is used to mount the turbine blade within the rotor assembly to a rotor wheel. The rotor wheel includes a plurality of circumferentially alternating dovetail slots and posts spread about the periphery of the rotor wheel. Each post is defined between adjacent dovetail slots. At least some known blades include internal cooling passages defined by the airfoil, platform, shank, and dovetail. In such blades, cooling fluid is supplied to the passages from a source of cooling fluid, such as compressor discharge air, coupled to the turbine blade.
At least some known turbine gas engines use a seal body that is typically positioned over the top of each rotor wheel post in a cavity bounded by the top of the post, the shank portions of adjacent blades and the underside of the platforms of adjacent blades. The seal body includes a forward cover plate that forms a cavity on the forward side of the rotor wheel. The temperature of the air within the forward cavity is generally hotter than the cooling air entering the dovetail portion of the blades due to leakage of hot gases from the primary gas stream into the forward cavity. As such, the forward cavity is typically purged with the cooling fluid. Thermal isolation of the top of the rotor wheel post ensures that the temperature of the rotor wheel post does not exceed allowable limits. The cover plates facilitate cooling of the rotor wheel, but the benefits of such cover plates may be outweighed by the requirement of additional space for the plates and the need for additional hardware components, which can increase the cost and decrease the performance of the gas turbine engine.
Accordingly, it would be desirable to improve rotor wheel cooling by channeling cooling air directly to the surface of the rotor wheel tangs, by reducing the number of hardware components needed, and by reducing the space requirements of the cooling system.